Vol. 1, No 1, 1994 pp. 3 - 11
UDC
533.9
ON THE POSSIBILITY OF THE THRESHOLD DRIFT INVERSION IN QPESIC INSTABILITIES IN WEAKLY IONIZED PLASMAS WITH ELECTRIC CURRENT FLOWING ALONG THE MAGNETIC LINES OF FORCE
B.S. Milić1 and D.Ž. Gajić2
1Faculty of Physics, P.O.B. 550, 11001 Beograd
2Faculty of Philosophy, Dept. of Physics, Ćirila i Metodija 2, 18000 Niš
Abstract. The process of spontaneous excitation of quasi-perpendicular ion-cyclotron (QPESIC) waves of growing amplitude by an electron drift parallel to the lines of force of the magnetization field is studied theoretically in uniform weakly ionized plasmas with one ion species. It is shown that, by an appropriate treatment of the ionic off-resonance terms in the dispersion equation, one arrives at the prediction of a drift-inversion effect, i.e. the possibility that, under certain circumstances, modes pertaining to higher-order ion- cyclotron (IC) harmonics may require smaller threshold drifts than those corresponding to the lower-order ones. In the theory presented herewith, the drift inversion takes place with Te/Ti ≈ 5, and becomes all the more prominent as Te/Ti is further increased. The effect is also dependent on the ion charge number zi, being more noticeable (setting in with lower values of Te/Ti) with doubly-charged ions than with the singly-charged ones. Most of these features seem to agree with certain experimental data.
PROBLEM DRIFTNE INVERZIJE KVAZI-POPREČNIH ELEKTROSTATIČKIH JONO-CIKLOTRONSKIH NESTABILNOSTI U SLABO JONIZOVANIM PLAZMAMA SA ELEKTRIČNOM STRUJOM DUŽ LINIJA MAGNETNOG POLJA
Teorijski se proučava proces spontanog pobuđivanja kvazi-poprečnih elektrostatičkih jono-ciklotronskih talasa narastajuće amplitude, uslovljenog prisustvom elektronskog drifta paralelnog magnetnim linijama sile u homogenoj, slabo jonizovanoj plazmi sa jednom vrstom jona. Pokazano je da se, adekvatnim tretiranjem vanrezonantnih članova u disperzionoj jednačini, dolazi do predviđanja efekta inverzije minimalnih driftova, tj. do mogućnosti da, pod izvesnim uslovima, jono-ciklotronski harmonik višeg reda može zahtevati manji minimalan drift nego harmonik nižeg reda. U teoriji koja je u ovom radu razvijena, inverzija minimalnih driftova nastupa kad je Te/Ti ≈ 5 i postaje sve izrazitija sa daljim porastom ovog odnosa temperatura. Efekt zavisi i od naelektrisanja jona, i primetniji je (nastupa pri manjoj vrednosti Te/Ti) kod plazme sa dvostruko naelektrisanim jonima nego kod one sa jednostruko naelektrisanim. Većina ovih osobenosti je, po svemu sudeći, u saglasnosti sa nekim eksperimentalnim podacima.
